For the recent years, camera devices, such as digital still cameras, employing solid state image sensors have become increasingly popular. In accordance with this, higher performance and miniaturized optics have been developed, which leads to a rapid popularization of much more downsized camera systems.
Evolution of optical systems toward much higher performance accordingly accelerates a demand for optical systems of much higher image quality and a demand for much greater magnification range optical systems, especially, extra great magnification range optical systems of which variable power ratio is greater than ×10. In addition, also strongly desired is downsizing not only of longitudinal extensions of optical systems along the optical axis but also of diameters of lens barrels; that is, optical systems satisfying all the needs and wants simultaneously are desired.
Prior art zoom lenses satisfying, to some extent, the needs and wants of higher image quality greater magnification range, and downsizing, include a compact zoom lens that provides the maximal angle of view exceeding 70 degrees and a variable power ratio of approximately ×10 or even greater, and still yet attains a satisfactory image quality as well as appropriate focusing, which comprises five lens groups, namely, a first lens group G1 of positive refractivity, a second lens group G2 of negative refractivity, a third lens group G3 of positive refractivity, a fourth lens group G4 of negative refractivity, and a fifth lens group G5 of positive refractivity where upon varying its operative posture from the wide angle end to the telephoto end to vary magnification, distances between the first and second lens groups G1, G2 and between the third and fourth lens groups G3, G4 become greater while distances between the second and third lens groups G2, G3 and between the fourth and fifth lens groups G4, G5 become smaller, and the third lens group G3 or part or subset of the lens group are displaced to permit the zoom lens be in infinity focus (e.g., see Patent Document 1 listed below).
Some other zoom lenses satisfying the aforementioned needs and wants to some extent include that which provides variable power ratio as great as ×7 to ×10, F number as great as 2.5 to 4, and sufficiently high performance to serve as an optical system suitable for the up-to-date image pick-up devices with the smallest pixel pitch, which is designed as a very compact high variable power zoom lens system and comprises the foremost or first lens group (Gr1) of positive refractive power, the succeeding or second lens group (Gr2) of negative refractive power, the third lens group (Gr3) of positive refractive power, and the rearmost or fourth lens group (Gr4) of negative refractive power arranged in a series, meeting the requirements defined in the formula as follows:1.1<f1/fT<2.5where f1 is a focal length of the first lens group (Gr1), and fT is a focal length of the whole optical system of the zoom lens photographing at its telephoto end (T) (e.g., see Patent Document 2 listed below).
Further other zoom lenses satisfying the aforementioned needs and wants to some extent include a zoom lens system that is sufficiently compact to incorporate in video cameras, digital still cameras, lens-integrated cameras, and the like, optimized for high-speed auto-focusing, and of enhanced image quality, which comprises the foremost or first positive power lens group, the succeeding or second negative power lens group, the third positive power lens group, the fourth negative power lens group, the fifth positive power lens group, and the rearmost or sixth negative power lens group arranged in a series where distances between the adjacent pairs of the lens groups are varied to vary power, meeting the requirements defined in the formulae as follows:DW(1-2)<DT(1-2)  (1)DW(2-3)>DT(2-3)  (2)DW(3-4)>DT(3-4)  (3)DW(4-5)<DT(4-5)  (4)DW(5-6)<DT(5-6)  (5)where DW(i-j) is a distance between the i-th and j-th lens groups when the zoom lens system photographing at its wide-angle end is in infinity focus. DT(i-j) is a distance between the i-th and j-th lens groups when the zoom lens system at its telephoto end is in infinity focus; and the fourth lens groups being displaced along the optical axis for focusing (e.g., see Patent Document 3 listed below).